Spinning Santa: North Pole gyrations

Q. At Christmas time, Santa can get so busy his head spins. Making matters worse, his house sits right on the North Pole. Why is this worse, and which direction does Santa's front door face, anyhow? – R. T. R. N. Reindeer

A. As the Earth turns, different points at different latitudes trace out larger or smaller circles through the day– roughly 25,000 miles at the equator, or just over 1000 miles per hour rotational speed, lesser circles and speeds moving toward the poles, say Arthur Upgren and Jurgen Stock in Weather: How It Works and Why It Matters.

By the time you get to Santa's place, it's not tracing out a circle at all, but turning on a dot, spinning around completely in the course of 24 hours, with a speed of zero. So "Santa Claus's house just rotates on itself, with every window (and door) facing south all the time." A truly dizzying Yuletide thought.

And here's another: What is Santa's house sitting on? poses Pennsylvania State University geoscientist Richard B. Alley. There's a big ocean out there. If his house is on the sea bed, that's fine. If it's on the sea ice, well, it's drifting across the Arctic Ocean and won't be at the North Pole much longer.

When a drill ship recently cored into the sea floor not far from the North Pole, they took along some icebreakers to run interference; as the ice drifted up, the breakers broke the ice to keep it away. "So maybe Santa has a fleet of icebreakers to keep the ice from sweeping his anchored-and-floating house away," Alley says.

Q.They come in a variety including plates, columns, stellars, needles, spatial dendrites, capped columns, and irregulars. They can be flat plates or the Christmassy type with feathery "arms." The Christmas type are idealized, since most in reality are "ugly sisters," with some 99 percent not even basically symmetrical.

Yet their classic symmetricality wooed the Chinese in 135 B.C. to comment on this, as did the Europeans at least by the Middle Ages. In the 17th century, the German mathematician Johannes Kepler pondered their beguiling six-sidedness, noting parallels with honeycombs and seed patterns inside pomegranates. Much later, Vermonter Wilson Alwyn Bentley grew obsessed, accumulating drawings of them by the hundreds, and in January 1885 completed his first successful photomicrograph of one.

If you know Bentley's nickname, you have the answer to this seasonal riddle. –F. T. Snowman

A. It was "Snowflake" Bentley, whose culminating book Snow Crystals was published in 1931, says Roger Highfield in The Physics of Christmas. The legacy of such work is the idea that no two snowflakes are identical, though a few years ago the U.S. National Center for Atmospheric Research found what appeared to be twin snowflakes, matching hollow hexagonal prisms.

They may have looked very similar, says Highfield, but a precise match is so unlikely as to be impossible. A snowflake might contain on the order of 100,000,000,000,000,000,000 water molecules. Just imagine the ways you could build a snowflake out of one hundred million million million water molecules.

"The short answer is, you can't," Highfield says. "Given near-freezing temperatures, light winds, and unstable convective atmospheric conditions, much larger and more irregular flakes can form," he adds. In January 1915, some four-inchers (in diameter) fell in Berlin, but the "real mother of all known flakes" fell on Fort Keogh, Montana, in January 1887, described as larger than milk pans ("Monthly Weather Review").

"It is claimed they measured 15 inches across and almost 8 inches thick," Highfield says.